The present invention relates to a charge and discharge system for electric power storage equipment, and a method of manufacturing the electric power storage equipment using the same.
In the manufacture of a lithium-ion secondary battery or nickel-metal hydride secondary battery, and the like, a charging treatment or a charging-discharging treatment of a unit battery is performed in order to inspect the secondary battery after assembling, or to activate chemical reactions, and so on. Conventionally, when a defective battery was found in the charging-discharging test of the batteries after assembling, it was necessary to select the defective battery individually. Therefore, the charging-discharging operation is performed on each battery individually by providing an independent charge and discharge power source for each battery.
In particular, a lithium ion secondary battery requires not only constant current charging, but also constant voltage charging during a charging operation. Therefore, an individual electric power source system for charging, which makes it possible to set the charging current and the charging voltage individually for respective batteries, is used.
On the other hand, when the battery is to be used for electric vehicles or batteries for electric power storage, a set of batteries is formed by connecting a plurality of unit batteries in series. The set of unit batteries connected in series is charged by applying a voltage at both end terminals, and voltage is discharged from both end terminals for taking out electric power. In a case when the set of batteries is charged or discharged under a condition wherein the batteries are connected in series, the same charging current flows through all the respective batteries. Therefore, if the capacity of one of the respective batteries differs somewhat from the other batteries, a variation in the voltage of the individual battery is generated.
Particularly, a lithium-ion secondary battery requires that the battery voltage be maintained at a value lower than a designated voltage during the charging operation. Therefore, a charge and discharge system, wherein a set of batteries connected in multi-series is charged or discharge, is well-known, as disclosed in JP-A-8-88944 (1996). In order to suppress the variation in the individual batteries connected in series, an electric power source is provided to the respective batteries for correction.
However, in the case when an individual unit battery is charged or discharged by a respective charge and discharge electric power source, a number of charge and discharge electric power supplies, which is proportional in number to the number of the unit batteries being charged or discharged simultaneously, are required. Particularly, the charge and discharge apparatus for activation treatment or inspection of the secondary batteries after assembling requires several hours for a series of charging-discharging operations. Therefore, in order to improve production efficiency, it is necessary to charge or discharge a large number of unit batteries simultaneously using a large number of charge and discharge electric power supplies. Therefore, a problem is generated in that a large number of the electric power supplies are required, in spite of the need only for charging or discharging a large number of unit batteries with a similar current and voltage pattern.
In accordance with the charge and discharge system, wherein plural unit batteries are connected in series for composing a set of batteries, and wherein the charging or discharging of the set of plural batteries is carried out simultaneously using an electric power source for the simultaneous charging or discharging, circuits for bypassing defective batteries which are detected during the charging or discharging operations are required for every one of the batteries. In order to charge or discharge the batteries so that the voltage of respective batteries becomes uniform by compensating a variation in voltage caused by variation in the capacity of a particular battery, a respective charge and discharge electric power source is required for each respective battery. In particular, for a lithium-ion secondary battery, it is necessary to perform charging or discharging while measuring the voltage of the respective battery precisely. In a condition under which each of the unit batteries is connected in series, the voltage of the respective battery must be detected by a differential voltage, and a problem arises in that the circuit for detecting the voltage becomes complex.
In a case when a plurality of batteries connected in parallel are charged or discharged, the charging current or discharging current does not become uniform, and so each of the batteries can not be charged fully. Furthermore, additional circuits for detecting a failed battery and separating the failed battery become necessary.